Current sensor

ABSTRACT

A sensor for use in detecting a time-varying current in a conductor ( 106 ) comprises plural sets of two oppositely-configured sensor elements ( 104 - 1 . . . 104 - 6 ) arranged around a sensing volume having a central axis, the sensor elements ( 104 - 1 A,  104 - 1 B) of each set being provided substantially in a common plane that does not intersect the central axis, and each set having a different common plane, the sensor elements of each set being arranged such that a normal (N) of their common plane at a point between central parts of sensor elements lies on a plane (P) that is radial to the central axis of the sensing volume.

FIELD OF THE INVENTION

This invention relates to a sensor for use in detecting a time-varyingcurrent in a conductor.

BACKGROUND

In the field of electrical distribution, it is useful to be able tomeasure current flowing through conductors. Often these conductors areoperated at high electric potential relative to ground and thus it isadvantageous to make the measurement without direct electricalconnection.

It is possible to make such measurements using a current transformer.Such a device uses a magnetic circuit to couple the current in theconductor to be measured (primary conductor) and the current in asecondary conductor. This magnetic circuit typically consists of a yokeof ferromagnetic material having a conductive coil (the secondaryconductor) wound therearound.

There are a number of drawbacks to this kind of current sensor. Themagnetic circuit may saturate either as a result of impedance in thesecondary circuit, the presence of a non-time varying current in theprimary conductor, or the presence of an externally imposed magneticfield. Any of these conditions results in the current sensor losingaccuracy. Furthermore, hysteresis in the magnetic circuit leads tonon-linear sensor response at low operating current.

Most modern current sensors can be constructed using surface coilsuniformly spaced around a central cavity through which the primaryconductor passes. These are known as Rogowski sensors. Rogowski sensorsinclude an air core, rather than a magnetic core. Surface coils includeone or more turns of a conductor provided on a substrate, for example byetching or using printed circuit board technology. In order to obtain agood rejection of magnetic fields that are not due to the primaryconductor, the surface coils are very precisely aligned on axes radialto a central axis of cavity through which the primary conductor passes.Such a sensor is described in U.S. Pat. No. 6,965,225 B2.

SUMMARY OF INVENTION

A first aspect of the invention provides a sensor for use in detecting atime-varying current in a conductor, the sensor comprising plural setsof two oppositely-configured sensor elements arranged around a sensingvolume having a central axis, a plane of zero sensitivity to uniformmagnetic fields of the sensor elements of each set being providedsubstantially in a common plane that does not intersect the centralaxis, and each set having a different common plane, the sensor elementsof each set being arranged such that a normal of their common plane at apoint between central parts of sensor elements lies on a plane that isradial to the central axis of the sensing volume.

This can result in the desirable effect of the responses of theoppositely-configured sensor elements can be cancellation of far fieldswhilst providing summation of a circulating field originating at theconductor. Moreover, sensors constructed in accordance with theinvention can offer rejection of external magnetic fields at least asgood as quadrupole element based sensors whilst producing signal levelscomparable with dipole based sensors.

The present invention provides a sensor arrangement which can be simplerand cheaper to manufacture. This is, at least in part, because sensorelements such as coils, which require precise planar alignment, are ableto be provided on a single planar substrate and thus inherently alignedin the same plane. Also, the sensor arrangement can be constructed withfewer substrates for a given number of coils, which potentiallycontributes to a simplified construction and reduced manufacturingcosts.

Including a regular arrangement of sensor elements can provide higherorder rejection to interfering fields, and produce nulls in the sensorresponse that can be arranged to coincide with the locations of specificconductors for which it maybe desirable that the sensor has no responsewhatsoever, for example conductors of other phases in a polyphasesupply.

The sensitivity of an arrangement in accordance with the invention canbe made to be largely uniform within the area enclosed by thesubstrates. In addition, the inclusion of additional sensor elements ona substrate can further improve the uniformity of the response withinthe sensor.

As will be seen from the below explanation, in the embodiments thesensor elements of each set are oppositely configured such that signalsinduced by a uniform magnetic field passing through the sensor elementsof the set have an opposite sign and such that signals induced by acirculating magnetic field due to a current passing through a conductorprovided in the sensing volume have the same sign. Also, the signalsinduced by the uniform magnetic field in the sensor elements of each sethave a first magnitude and the wherein the signals induced by thecirculating field in the sensor elements of each set have a secondmagnitude.

Each of the oppositely-configured sensor elements in each common planemay be provided on a respective common substrate. Alternatively, theoppositely-configured sensor elements may be supported on respectivesubstrates, or may be supported in place by some other suitable means.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating principles by which theinvention operates;

FIG. 2 depicts an example of a set of two oppositely-configured sensorelements of which embodiments of the invention are comprised;

FIG. 3 is a schematic view of a sensor arrangement according to a firstembodiment of the invention;

FIGS. 4A and 4B depict sets of two oppositely-configured sensor elementswhich may be used in alternative embodiments of the invention;

FIG. 5A shows a far-field sensitivity pattern of a sensor according tothe first embodiment of the invention;

FIG. 5B shows a pattern of uniformity within a sensor according to thefirst embodiment of the invention;

FIG. 5C shows the rejection of sensitivity to an interfering conductoras a function of distance of a sensor according to the first embodiment;

FIGS. 6A and 6B show a sensor device constructed according to the firstembodiment of the invention; and

FIGS. 7A-C depict alternative embodiments of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the drawings and the below-described embodiments, like referencenumerals refer to like elements.

FIG. 1 depicts a primary conductor 100, a circulating magnetic field Bresulting from a current I flowing through the primary conductor 10 anda schematic view of a set of two oppositely-configured sensor elements104 of which the invention is comprised.

In FIG. 1, a current is flowing through the primary conductor 100 in adownwards direction, as denoted by the arrow labelled I. Current movingthrough the primary conductor 100 results in a circular magnetic fieldloop B surrounding the primary conductor 100. The direction of themagnetic field at particular positions on the loop B are denoted by thearrows B1 and B2.

The sensor elements 104A, 104B of the set of sensor elements 104 areconfigured such that when a uniform field, such as due to a distantcurrent carrying conductor (not shown), passes through the sensorelements 104A, 104B, equal and opposite signals are produced byinduction in each of the sensor elements 104A, 104B. As such, the sum ofthe signals generated by the set of oppositely-configured sensorelements 104 due to a uniform field is zero. The magnetic field loop Bdue to the primary conductor B, however, passes through a first of thesensor elements 104A in a first direction B1 and through a second of thesensor elements 104B in a second, opposite direction. Thus, instead ofcancelling (as was the case with signals induced due to a uniformmagnetic field), the signals induced in the set of oppositely-configuredsensor elements 104 sum positively. It will thus be understood that theset of two oppositely-configured sensor elements 104 is arranged suchthat the signals due to a uniform magnetic field passing through each ofthe pair of sensor elements 104A, 104B cancel and that signals inducedby the magnetic field loop due to the primary conductor 100 in each ofthe sensor elements 104A, 104B are equal and of the same sign (and thussum positively).

FIG. 2 shows a set of oppositely-configured sensor elements 104 of whichsome embodiments of the invention are comprised.

The two sensor elements 104A, 104B of the set 104 are providedsubstantially in a common plane. In this example, the sensor elements104A, 104B are provided on a surface of a planar substrate 200. Thesensor elements 104A, 104B each consist of one or more turns of aconductor. In this example, the sensor elements 104A, 104B consist ofplural turns of a conductor provided on the surface of the substrate200. The sensor elements 104A, 104B have a plane of zero sensitivity touniform magnetic fields is coincident with the plane of the substrate200 a

The sensor elements 104A, 104B, which may also be termed dipole coils,are oppositely-configured by virtue of the direction in which the one ormore turns are wound. For example, in FIG. 2, the first sensor elementwinds from the centre outwards in a clockwise direction. Conversely, thesecond sensor element winds from the centre outwards in an anticlockwisedirection. A set of two oppositely configured sensor elements 104 mayalso be termed a quadrupole coil set. The terms dipole and quadrupolerefer to the magnetic arrangement that arises from the coils.

FIG. 3 shows a sensor arrangement 300 of plural sets of twooppositely-configured sensor elements 104-1 to 104-6 according to afirst embodiment of the invention. Each set of two oppositely-configuredsensor elements 104 is provided on a planar substrate (not labelled inthe Figure) and may be referred to as a sensor board (also labelled104-1 to 104-6). Each sensor elements 104 has a plane of zerosensitivity to uniform magnetic fields that is coincident with the planeof its sensor board 104-1 to 104-6.

The sensor arrangement 300 according to the first embodiment of theinvention comprises six sensor boards 104-1 to 104-6. The Figure alsoshows the primary conductor 100, which in this example has a currentflowing through it in a direction into the page. Also shown is thecircular magnetic field loop (the direction of the field being denotedby arrows around the circle) due to the current flowing through theprimary conductor 100.

The plural sensor boards 104-1 to 104-6 are arranged around the primaryconductor 104. The sensor boards 104-1 to 104-6 are arranged such that avolume V is encapsulated by the sensor boards 104-1 to 104-6 around theprimary conductor 100. Each of the sensor boards 104-1 to 104-6 isarranged such that a normal N to the plane in which a set ofoppositely-configured sensor elements 104 lies (i.e. the plane of thesurface of the substrate on which the sensor elements 104A, 104B areprovided) at a point on the plane between two oppositely configuredsensor elements (for example, sensor elements 104-2A and 104-2B) lies ona plane P that passes through a central point of the volume Vencapsulated by the sensor boards. Optimally, the sensor elements (forexample sensor elements 104-2A and 104-2B) are symmetric about thenormal N to the plane of the sensor elements which lies in the plane Pradial to the central point of the volume V.

Each of the sensor boards 104-1 to 104-6 overlaps at each end with oneof the other sensor boards 104-1 to 104-6 such that each sensor board104 comprises two end portions 302, 304, which extend beyond therespective overlapping other sensor boards 104, and a middle portion 306extending between the two end portions 302, 304. In this example, thesensor elements 104-1A, 104-1B etc are provided on the end portions 302,304 of the sensor boards 104.

The sensor boards 104 are arranged such that signals due to the circularmagnetic field in each of the sensor elements 104-1A, 104-1B etc sumspositively. Each of the sensor elements 104-1A, 104-1B is connected inseries with an adjacent sensor element. As such, a first sensor element104-1A of a first sensor board is connected in series with a secondsensor element 104-6B of a sixth of the sensor boards 104-6 which isthen connected in series to a first sensor element 104-2A of a secondsensor board 104-2 and so on.

The sensor elements 104-1A, 104-1B etc may be connected using printedtracks on a rigid or flexible circuit board or by using twisted pairwiring. Alternatively, the sensor elements 104-1A, 104-1B etc may beconnected in parallel, although in such embodiments the sensor elements104-1A, 104-1B etc require matched resistances.

The sensor boards 104 optimally are arranged such that a cross-sectionof the volume surrounded by the sensor boards is of a regular polygonalshape, in this embodiment, a hexagon.

FIGS. 4A and 4B show alternative sensor boards that may be used to formembodiments of the invention.

FIG. 4A shows a front and a back respectively of a first alternativesensor board 404. Turns of conductive material are provided on each sideof the sensor board 404. The turns of conductive material at each end ofthe sensor board are connected by a via 400 passing through thesubstrate 408 of the sensor board. The turns are arranged such that thesignal due to a magnetic field passing through the turns provided at afirst end of the front of the sensor board sums positively with theturns provided on the first end of the back surface of the sensor board.Thus, in this example a single sensor element 404A, 404B comprises theturns on both the front and the back of the sensor board 404. Theprovision of turns of conducting material on both sides of the sensorboard increases the sensitivity of the sensor element 404A, 404B to acircular magnetic field.

FIG. 4B shows a second alternative sensor board 406. In this example,the sensor board 406 includes the oppositely-configured primary sensorelements 104A, 104B (as described with reference to FIG. 2) and also aset of two oppositely-configured additional sensor elements 402. Theadditional sensor elements 402 have an effect of improving theuniformity of the response within the sensor arrangement. The additionalsensor elements 402-1, 402-2 are provided on a middle portion 306 of thesensor board 406. The additional sensor elements 402-1, 402-2 alsocomprise one or more turns of conductive material and areoppositely-configured by virtue of their direction of winding. Theadditional sensor elements 402-1, 402-2 have a plane of zero sensitivityto uniform magnetic fields that is coincident with the plane of theirsensor board 406.

It will be understood that, according to some examples, the sensorboards may comprise more that one set of two oppositely-configuredadditional sensor elements. Also, it will be appreciated that theprimary sensor elements 104A, 104B and the additional sensor elements402-1, 402-2 of the sensor board of FIG. 4B may also include turns ofconductive material on the opposite surface of the sensor board, such asis described with reference to FIG. 4A.

The sensor boards may be multi-layer circuit boards incorporatingelectrostatic shielding layers. A shielding layer protects the sensorelements from electrostatic pickup from the voltage on the conductor,when measuring the current in the conductor.

The sensor elements may be fabricated using any means of producingcoplanar circuit elements such as printed circuit board technology,integrated circuit fabrication, thick film techniques and screenprinting. Alternatively, the sensor elements may printed on ceramic orglass or may comprise pre-wound turns of conductive material held inplace on a former or embedded in a moulding.

FIG. 5A shows a far-field sensitivity pattern from a sensor arrangementcomprised of the sensor boards 406 described with reference to FIG. 4Band arranged according to the first embodiment as described withreference to FIG. 3. Each of the lines on FIG. 5A shows positions ofzero sensitivity to far magnetic fields around the sensor arrangement300. The far-field rejection is a function of the order of symmetry ofthe arrangement of the sensor elements. The sensor arrangement of FIG.3, which includes six boards and therefore 12 sensor elements, producesa far-field sensitivity pattern having 24 null response directions. Anarrangement comprised of four sensor boards arranged in a squareprovides a far-field rejection pattern exhibiting 16 null responsedirections. A sensor arrangement made up of three sensor boards arrangedin a triangle produces a far-field sensitivity pattern including 12 nullresponse directions.

FIG. 5B shows the pattern of uniformity within a sensor arrangementhaving six sensor boards 406 such as that shown in FIG. 4B which arearranged according to the first embodiment described with reference toFIG. 3. The lines on the Figure show the positions of a 0.1% deviationin sensitivity. An arrangement of six sensor boards, which has six setsof oppositely-configured sensor elements 104A, 104B (i.e. resulting insix quadrupoles) has at best 12 radial planes of uniform sensitivity tocurrent flowing within the volume surrounded by the sensor boards. Theprovision of additional sensor elements 402-1, 402-2 on the sensorboards 406 improves the uniformity of the response within the sensorarrangement. For example, introducing onto each sensor board twooppositely-configured additional sensor elements 402-1, 402-2 (i.e. oneadditional quadrupole) increases the number of planes of uniformsensitivity by a factor of three. Thus, as can be seen in FIG. 5B, sixsensor boards each having a set of primary sensor elements 104 resultsin 12 planes of uniform sensitivity which, due to the provision of a setof additional sensor elements 402 on each sensor board 406 is multipliedby three to result in 36 planes of uniform sensitivity.

FIG. 5C shows, for the sensor arrangement 300 of FIG. 3 incorporatingthe sensor boards of FIG. 4B, the rejection of sensitivity to aninterfering conductor as a function of distance from the centre of thevolume V. The worst case is measured at a location halfway between thenulls in sensitivity of FIG. 5A.

FIGS. 6A and 6B depict a schematic plan- and side-view respectively of asensor device 600 according to the first embodiment of the invention.The sensor boards 406 are arranged to provide a hexagonal volume throughwhich the primary conductor 100 extends. The sensor boards 406 areprovided in a rigid frame 600. The rigid frame comprises top and bottomportions 600-1, 600-2 which may be connected together for example usinga plastic bolt(s) (not shown) which pass(es) from the top portion 600-1to the bottom portion 600-2 of the frame 600. The frame may have slots(not shown) for supporting the edges of the sensor boards 406.Alternatively the edges of the sensor boards 406 may held against theinner surfaces of the top and bottom portions 600-1, 600-2 of the frame600. According to alternative embodiments, the sensor boards 406 may beinsert moulded. The sensor device of FIGS. 6A and 6A may also includesignal conditioning electronics components (not shown) provided on thesensor boards.

FIGS. 7A-C depict arrangements of sensor boards 406 according toalternative embodiments of the invention. The arrangement 700 of FIG. 7Aincludes four sensor boards 406 arranged so as to encompass a squarevolume around the primary conductor 100 and provided such that signalsinduced in the sensor elements (not shown) due to the circular magneticfield sum positively.

FIG. 7B shows a sensor arrangement 702 including three sensor boards 406arranged such that they encompass a volume having triangularcross-section. As in the embodiments of FIGS. 3 and 7A, the sensorboards are arranged such that the signals generated in the sensorelements (not shown) due to a circular magnetic field sum positively.

FIG. 7C shows an arrangement according to an alternative embodimentincluding two sensor boards 406 arranged around a primary conductor 100.

The sensor boards of FIGS. 6 and 7 have been denoted as sensor boards406 (i.e. those described with reference to FIG. 5B). However, it willbe appreciated that they may instead comprise other types of sensorboards, for instance, but not limited to, those described with referenceto FIGS. 2 and 4A.

In the above, the oppositely configured sensor elements are oppositelywound coils. These provide the function of giving an output signal ofopposite sign for a uniform field. If the oppositely configured sensorelements are matched, for instance by having symmetrical configurations,they provide the function of giving an output signal of opposite signand magnitude for a uniform field.

In other embodiments, the oppositely configured sensor elements are Halleffect sensors with different configurations, such that they give anoutput signal of opposite sign for a uniform field. In these cases, thesensors have planes of zero sensitivity to uniform magnetic fields, thatare aligned similarly to the planes of the coils described above. Instill further embodiments, electronic circuits are applied to sensorelements that have the same physical construction so as to cause them tobe oppositely configured.

It will be understood by the skilled person that the any other suitableoppositely configured sensor elements could be used with the invention.

It should be realized that the foregoing embodiments should not beconstrued as limiting. Other variations and modifications will beapparent to persons skilled in the art upon reading the presentapplication. Moreover, the disclosure of the present application shouldbe understood to include any novel features or any novel combination offeatures either explicitly or implicitly disclosed herein or anygeneralization thereof and during the prosecution of the presentapplication or of any application derived therefrom, new claims may beformulated to cover any such features and/or combination of suchfeatures.

1. A sensor for use in detecting a time-varying current in a conductor,the sensor comprising plural sets of two oppositely-configured sensorelements arranged around a sensing volume having a central axis, a planeof zero sensitivity to uniform magnetic fields of the sensor elements ofeach set being provided substantially in a common plane that does notintersect the central axis, and each set having a different commonplane, the sensor elements of each set being arranged such that a normalof their common plane at a point between central parts of sensorelements lies on a plane that is radial to the central axis of thesensing volume.
 2. The sensor of claim 1, wherein the sensor elements ofeach set are substantially symmetric about the point that lies on theplane that is radial to the central axis of the sensing volume.
 3. Thesensor of either preceding claim, comprising at least three sets of twooppositely-configured sensor elements arranged such that the sensingvolume has a substantially regular polygonal cross-section.
 4. Thesensor of any preceding claim, comprising one or more sets each of twooppositely-configured compensation sensor elements provided in the planecommon to a first set of two oppositely-configured sensor elements. 5.The sensor of claim 4, wherein: at least one of four or moreoppositely-configured sensor elements in a first common plane is locatedon the side of a second common plane of other elements that is oppositeto the central point, and at least three of the fouroppositely-configured sensor elements in the first common plane arelocated on the side of the second common plane that is closest to thecentral point.
 6. The sensor of claim 5, wherein theoppositely-configured compensation sensor elements in the first commonplane are located on the side of the second common plane that is closestto the central point.
 7. The sensor of any preceding claim, wherein atleast two of the oppositely-configured sensor elements in a common planeare provided on a common substrate.
 8. The sensor of any precedingclaim, wherein each of the oppositely-configured sensor elements in eachcommon plane is provided on a respective common substrate.
 9. The sensorof any preceding claim, wherein each of the sensor elements comprisesone or more turns of a conductor.